Vault alarm system



Jan. 16, 1968 v. T. MCDONOUGH 3,364,477

VAULT ALARM S YSTEM 4 Sheets-Sheet l Filed F'eb. l5, 1965 Jan. 16, 1968v T, MCDONOUGH 3,364,477

VAULT ALARM SYSTEM 4 Sheets-Sheet 2 Filed Feb. l5, 1965 Jan. 16, 1968 v.T. MCDONOUGH '3,364,477

VAULT ALARM SYSTEM 4 Sheets-Sheet 5 Filed Feb. l5, 1965 303m mmm Jan.16, 1968 V. T. MCDONOUGH 3,354,477

VAULT ALARM SYSTEM Filed Feb. l5, 1965 4 Sheets-Sheet 4 D! Lu [E U LL] DE J Z L I I I I I I I I I I I I I I l l U Z u.: D C LLI f u.

.LndlnO FIG. 4

United States Patent Office 3,354,477 Patented Jan. 16, l68v 3,364,477`VAUL'lF ALARM SYSTEM Vincent T. McDonough, Verona, NJ., assignor toAmerican District Telegraph Company, `Iersey City, NJ., a corporation ofNew Jersey Fiied- Feb. 15, 1965, Ser. No. 432,646 5 Claims. (Cl.340-261) ABSTRACT F THE DISCLSURE An alarm sys-tem of the soun-dmonitoring type for the protection of vaults affording superiorprotection against attacks designed to elude the responsecharacteristics of such systems of the prior art and a reduc-tion in thepossibility of the production of false alarm signals. The system employsa preamplifier and a peaking circuit, the output of which is supplied toa continuous channel and an impact channel. The latter provides avoltage pulse output proportioned in amplitude and duration to values ofthe signal voltage passed by a thresh-old control. The output of bothchannels is applied to an integrating circuit. An alarm is produced whenthe energy stored in the integrating circuit exceeds a predeterminedvalue.

The present invention relates to burglar alarm systems, and moreparticularly to burglar alarm system of the type especially adapted forthe protection of vaults and similar enclosures.

Burglar alarm systems for vaults and the like operating on` theprinciple of noise detection have been used for many years, and avariety of such systems have been proposed. One type comprises thosealarm systems designed to be responsive primarily to the vibrationsproduced within the walls and other structure of a Vault by aburglarious attack thereon rather than to airborne noises. Systems ofthis type, particularly when employed in conjunction with means forintegrating or accumulating the effects of detected sounds have beenproved effec-tive and U. S. Patent 3,147,467, issued Sept. l, 1964, toPeter Laakmann is an example o-f such a system.

A particular feature of the above mentioned Lankmann patent is the dualchannels provided for the integration of detected vibrations. Onechannel, termed the integrating channel, is designed to detect sounds oflow intensity but prolonged duration and, by integrating the totalenergy represented by such sounds, initiate an alarm indication when theaccumulated energy level is deemed to be representative of a genuineattack upon the protected vault. The integration effect, plus frequencydiscrimination, make it possible for the integrating channel todiscriminate successfully between the sounds of a bona fide attackconducted by a relatively quiet tool such as an electric drill wit-h adiamond tipped cutter and the innocuous sounds of ordinary activity inthe vicinity. The disturbing effect of false alarms is thereby avoidedor minimized without sacrificing responsiveness to real attacks. Sincethe possibility exists that a high intensity sound of short durationsuch as a dynamite blast could overdrive the amplifier and there'by failto produce an alarm signal, an impact channel was provided to bypass theintegrating channel and actuate the alarm signal directly upon theoccurrence of a high intensity sound.

Systems yof the foregoing type have been placed in service and whilefound to be generally satisfactory, have suffered from a tendency toproduce false alarms upon a dip in the voltage of the power supply andby response of the impact channel to a single sound of moderateintensity as that resulting from a vehicle in a parking lot striking theside of the building containing the protected vault.

In addition, the six-stage amplifier with multiple feedback circuitsmakes the electronic equipment both complex and costly with attendantdifficulty in routine servicing operations.

The principal object of the present invention has been to provide anovel and improved vault alarm system of the acoustical type.

An impor-tant feature of the present invention is the ability t-o resistdefeat by an attack consisting of a number of l-ow energy blowsdelivered at spaced intervals. The earlier system is, a-t leasttheoretically, susceptible to cornpromise by a series of blows, each oflow enough energy to escape detec-tion by the impact channel andsufficiently spaced in delivery time so that the normal discharge timeconstant of the integrator will prevent the accumulated energy fromreaching the alarm level. The present invention, by providing means tointegrate the effect of impact sounds, is far less susceptible to suchattack and consequently exhibits a greater dynamic range.

A further feature of the invention is the provision of threshold meansand pulse generating and amplifying means in the impact channel wherebythe evolution of false alarm indications from a single impact ofmoderate energy are avoided without sacrificing the detection of theimpact sounds of a bona fide attack.

Another object of the invention has been the provision of a sensitivevault protection system which is resistant -to spurious alarms due toinnocuous sounds but requiring relatively simple electronic circuitryand a minimum number of stages of amplification.

A feature of the invention is the means provided whereby the responsecharacteristics of the amplifier are specially tailored to detectorelements in such manner as to maximize the signal-to-noise ratio.

Still another object of the present invention has been the provision ofan electronic vault protection system which is not subject to .theevolution of false alarm indications upon the occasion of briefreductions in the voltage of the power supply.

The electrical protection system of the invention detects physicalattacks on a vault or strong room intended for the safekeeping ofvaluables and comprises vibration transducer means physically disposedrelative to the structure to be protected so as to produce a signalvoltage proportional to the energy expended in an attack upon thatstructure, integrating means coupled to the transducer means andarranged continuously to average the signal voltage over a predeterminedrelatively long time interval, and alarm signalling means coupled to theintegrating means and arranged t-o produce an alarm signal indicationwhen the integrated voltage exceeds a predetermined level.

Other and further objects, features and advantages of the invention willappear more fully from the following description of the invention takenin connection with the appended drawings, in which:

FIG. l is a block diagram of a system embodying the invention;

FIGS. 2 and 3, when joined together, area schematic illustration of acircuit arrangement embodying the in-vention;and

FIG. 4 is an illustrative plot o-f output versus frequency for use inexplaining certain principles of the invention.

Referring now to FIG. l, the system input is derived from the interiorsurface of the vault to be protected by means of vibration transducers2G. The vibration transducers, a number of which are preferablyconnected in parallel, are mounted in direct contact with the internalsurface of the vault, preferably in an equally spaced pattern.Typically, twelve transducers might be used, although the number may bevaried to suit particular requirements.

The vibration transducers are preferably microphones of thepiezoelectric type and may each comprise direct actuated Rochelle saltcrystal elements arranged in Bimorph construction and housed in adie-cast metallic casing. To insure reliable sensitivity over largeambient temperature and humidity ranges, the vibration transducer casemay be sealed in a suitable potting compound such as an epoxy resin witha hardening agent so that vibratory energy will be transmitted to thecase and from the case to the crystal elements within the case.Enclosing the vibration detecting elements also serves to shield theseelements from airborne sounds except as the latter may producevibrations in the vault structure. Vibration transducers other thanthose of a crystal type may be used, although the crystal type ispreferred.

When any one or more of the vibration transducers are subjected to anacceleration, which will occur when the surface to which the transduceris attached vibrates, an alternating voltage will be produced. Thisalternating voltage is applied to a preamplifier 21 which increases thesignal sufiiciently to permit subsequent operations. The signal is thenpassed to the peaking circuit 22, which will be more fully describedhereinafter, for the purpose of maximizing the signal-to-noise ratio. Amaximum signalto-noise ratio is important to permit operation with aminimum number of stages of amplification. The optimized signal is thenamplified at 23 and passed to the channel divider 24. From this point,the signal is processed either by the continuous channel 25 or theimpact channel 26 depending upon the characteristics of the sounddetected.

If the sound is of low intensity but sustained duration as would resultfrom the operation of an electric drill, the signal will pass throughthe continuous channel 2S. If the sound is of an impact nature such as asledge hammer blow, the resultant signal will be processed by the impactchannel 26.

In the continuous channel the signal first passes to the sensitivitycontrol 27 which controls the amplitude of the signal and consequentlythe alarm reaction time for a given level of attack signal. The modifiedsignal is then amplified at 28, fed to a rectifier and voltage doublercircuit 29 and thence to an integrator 39.

impact signals pass from the channel divider 24 to a rectifier 31 andthen to a threshold control 32 which controls the amplitude of thesignal and consequently the intensity of impact sound required toinitiate an alarm signal indication. The modied signal is then appliedto a pulser-amplifier 33 where the pulse to be fed to integrator 30 isgenerated.

The integrator 3@ averages the signal inputs over a suitable timeinterval, preferably about -25 minutes. Thus the output of theintegrator is proportional to the average wall vibrations over aselected period regardless of whether the input is derived from thecontinuous channel or the impact channel. It should be understood thatthe longer the time interval over which the averaging occurs the lesslikely it will be that an attack will be undetected, since even anextremely slow attack will eventually produce a substantial integratedoutput.

The output of integrator 30 is supplied to a voltage sensitive detector34 which actuates an alarm relay 35 when the voltage reaches apredetermined level. The alarm relay may conveniently be provided with aset of transfer contacts which control the operation of conventionalalarm signal indicators, It is highly desirable that the alarm signal betransmitted to a central station, guard station or police headquarters,but a local audible or visual alarm may be provided as is well known inthe art.

Interposed between the voltage sensitive detector and the alarm relay isa suppressor circuit 36 whose function is to prevent the initiation offalse alarm signal indications upon the occurrence of a decrease in thevoltage of the power source.

The detailed operation of a circuit embodying the principles of thepresent invention will now be described in conjunction with FIGS. 2 and3 wherein typical values of the resistors and capacitors are shown inohms and microfarads respectively, within brackets adjacent to thepictorial representation of the circuit component. Vt/hile specificvalues of the various components as well as operating voltages will bereferred to in the following description, they are intended forillustrative purposes only and not as limitations of the presentinvention.

The vibration transducers 2@ are connected in parallel between theshield and the conductor of a shielded coaxial microphone cable 37. Theconductor of the shielded cable is connected to the high side of theprimary winding of an impedance matching transformer TF1 While theshield is connected to the other side of the primary winding and toground at 38. One side of the secondary winding of transformer TF1 isconnected vto the base of a transistor T1 which forms the preamplifier21 while the other side is connected to a point between resistor R1 andthe parallel combination of resistor R2 and capacitor C1. Resistor R3,connected across the secondary winding of transformer TF1 helps reducethe noise level while capacitor C2, connected between the low sides ofthe primary and secondary windings provides a path to ground 38 forunwanted alternating current signals which may be induced in theapparatus by extraneous sources.

The series combination of resistor R1 and resistor R2 is connected atone end to a positive voltage supply conductor 39 and at the other endto a negative voltage supply conductor 40. Conductors 39 and itl arecoupled to voltage supply input terminals i1 and 42 through resistorsR4, R5, rectifier REC 12 and rectifier circuit 43 which comprisesrectiers REC 1, REC 2, REC 3 and REC 4 arranged to maintain thepolarities of conductors 39 and itl irrespective of the supply voltagepolarity. The supply voltage typically might be 25 volts, D.C. andrectiers REC 1 through REC 4 conveniently might be of the IN 2070 type.Resistors R4, R5 and capacitors C3, C4 comprise a lter network to smooththe supply voltage while a diode REC 5 which might conveniently be ofthe IN 30248 type is connected between conductors 39 and 4i) forprotection in the event of voltage surges in the supply. The potentialbetween conductors 39 and 40 would be typically 15 volts.

The circuit network of resistor R1, resistor R2 and capacitor C1 furnisha forward bias voltage for the preamplifier transistor T1 which might beconveniently of the TI 495 type. The emitter of transistor T1 is coupledto conductor 40 by the parallel combination of a resistor R6 and acapacitor CS which, together with the preceding network, establish theoperating point of transistor T1. The collector of transistor T1 iscoupled to conductor 39 by means of a tap on the primary winding of atransformer TF2 and the parallel combination of a resistor R7 and acapacitor C6 connected across the primary winding of transformer TF2.One side of the secondary winding of transformer TF2 is connected to thebase of a transistor T2 While the other side is connected to thejunction of resistors R1 and R2.

The components in the collector circuit of transistor T1 comprise thepeaking circuit 22. Capacitor C6 and transformer TF2 constitute a tunedcircuit whose frequency response is designed to match the naturalfrequency response characteristic of the vibration transducers. Thesolid line curve of FIG. 4 depicts the typical response of a transducercomprising a major output peak followed by several lesser peaks as thefrequency of the input sound increases. The corresponding responsecharacteristic of the peaking circuit 22 is shown as the dashed linecurve and it will be noted that capacitor C6 and transformer TF2 havebeen so selected as to provide peak response at a frequencycorresponding to the major peak of the transducer response curve.Furthermore, the peaking circuit curve has been made asymmetric so thatthe right hand side will embrace the minor peaks of the transducercurve. Still another modification to the peaking circuit response hasbeen the provision of the resistor R7 whose function is to broaden thepeak of the peaking circuit curve sufficiently to allow for the normalvariations in characteristics to be expected between individuals of anumber of vibration transducers. The practical purpose of the shaping ofthe peaking circuit response is to improve the signal-to-noise ratiowhich, in turn, permits operation of the entire apparatus at the desiredsensitivity level with far fewer stages of amplification than have beenrequired in the prior art. It is desirable that the peaking circuiteffectively suppress usual ambient noise frequency components in thetransducer outputs. For this purpose the peaking circuit should cut ofifrequency components below about 1000 cycles per second.

The signal output of preamplifier Z1, after shaping by the peakingcircuit 22, is applied to the base of a transistor T2, which mightconveniently be of the TI 495 type, and which comprises the amplifier23. The network of resistor R1 and resistor R2 plus capacitor C1establish the forward bias voltage for transistor T2 and, together withresistor R8 and capacitor C7 in the emitter circuit of transistor T2determine the operating point of transistor T2. The collector circuit oftransistor T2 is coupled to conductor 39 through the primary winding ofa transformer TF3, which, with its double wound secondary, constitutesthe channel divider 24 and provides for maximum signal transfer.

The high side secondary winding 44 is a portion of the continuouschannel 25 and has one end connected through a potentiometer R9 to thebase of a transistor T3 while the other end is connected to the junctionof resistors R-R11 and to the junction of resistor R9 and capacitor C8.Signals representing sounds of a continuous nature such as thoseproduced by the operation of an electrical drill or prolonged hammeringof relatively low intensity are applied, after shaping in the peakingcircuit 22, to the base of transistor T3, which is the amplifier 28 ofthe continuous channel 25, through the potentiometer R9 that comprisesthe sensitivity control 27. The amplitude of the signal in thecontinuous channel is controlled by potentiometer R9. The setting ofpotentiometer R9 establishes the length of time a signal of givenamplitude must persist to initiate an alarm indication. Signalsrepresenting sounds of an impact nature will also be applied to thecontinuous channel, but because of their short duration and the factthat their relative amplification in amplifier 28 will be small ascompared to the amplification accorded to the lower amplitude signals,these impact signals will not have an undue alarm producing effect onthe continuous channel.

The forward bias voltage for transistor T3, which also might be of theTI 495 type, is supplied by the network comprising resistor R10 andresistor R11 plus capacitor C8 which, together with resistor R12 andcapacitor C9 in the emitter circuit, establish the operating point fortransistor T3. A transformer TF4 whose primary winding connects thecollector of transistor T3 to conductor 39 supplies the amplified signaloutput of transistor T3 to the rectifier-doubler 29. The low side of thesecondary winding of transformer TF4 is connected directly to conductor40 while the high side is coupled through a capacitor C10 to thejunction of rectiers REC 6 and REC 7 which both might conveniently be ofthe IN 2070 type. The cathode of rectifier REC 6 is connected directlyto conductor 40 while the anode of rectifier REC 7 is connected toconductor 40 through a capacitor C11. The combination of capacitor C10and rectifiers REC e and REC 7 comprise the full wave rectifier-voltagedoubler 29 whose output is stored in capacitor C11.

A resistor R13 is connected across the capacitor C11 to form, withcapacitor C11, the integrator 30. All incoming signals from thecontinuous channel 25 are integrated over an interval determined by thetime constant of resistor R13 and capacitor C11 (4.7 meg. 250

mf.=19.5 minutes). Thus the output of integrator 30 represents theaverage of all signals received during that period. While for practicalpurposes an integrating time interval of about 20 minutes is preferred,an integration time interval of as little as one-half minute willprovide improved results over systems without this feature. On the otherhand, an integrating time interval of as much as several hours might beused to advantage in special cases where an extremely slow rate ofattack was possible.

A violent attack, as for example a dynamic blast, while of highintensity, may also be of such short duration as to provide insufficientsignal energy to raise the integrator circuit output to the alarm level.As noted above, a high intensity signal will not receive the samerelative amplification as a continuous signal. In this regard it shouldbe noted that a typical continuous attack signal at the transduceroutput might be of the order of 20 microvolts while an impact alarmsignal at the transducer output typically might be of the order of 2volts. To guard against loss of impact alarms of short duration, animpact channel 26 has been provided that represents distinct advantagesand improvements over similar features of the prior art. The impactchannel of the previously identified Laakmann patent was subject tofalse alarms resulting from single impact blows of innocuous nature ascaused by a workman dropping a tool or a vehicle striking the exteriorof the building containing the protected vault. The present inventionovercomes the tendency toward false alarms without sacrificing theability to detect genuine attack by the provision of a threshold device,a pulse circuit and routing of impact signals through the integrator asexplained below.

The impact channel 26 begins with the low side secondary winding 45 oftransformer TF3 whose upper side is connected to conductor 40 through -arectifier REC 8 which might be of the 1N 2070 type. The lower side isconnected to the base of a transistor T4 'through a rectifier REC 9which also might be of the IN 2070 type. Rectifier REC 9 and capacitorO12, which is connected across secondary winding 45, comprise therectifier network 31 which converts signals representing impact soundsto direct current. The rectifier network 3'1 in conjunction vvith thevariable resistor R14, which connects the -emitter of transistor T4 toconductor 40, determines the collector current of transistor T4.Transistor T4, which might conveniently be of the TI 495 type, togetherwith rectifier REC 9 and resistor R14, constitute the threshold control312.

The function of the threshold control is to establish a signal levelwhich must be exceeded before energy can be passed to the integrator sothat random, individual sounds may be prevented from producing falsealarms. Since the desired signal level will vary from one installationto another and, indeed, from time to time in a particular installation,'the variable resistor R114 is provided so that suitable adjustments maybe made. The series combination of resistor R15 and rectifier REC 8which connects the collector circuit of transistor T4 to conductor `40tends to reduce the threshold but is primarily provided to compensatefor the effect of temperature variation-s on the base-emitter junctionof transistor T4. Resistor R116 connected across the secondary winding45 is intended to minimize 4the etiect of temperature induced variationsin the collector-'base current of transistor T4 on the collectorcurrent. A typical threshold voltage (baseemitter of transistor T4)might be in the range of Z50 to 300 microvolts. Considered in anotherway, the threshold level for the impact channel typically might be 25 dbabove the usual alarm signal level for the impact channel.

Resistors R17 and RdS are in series connection between the collector oftransistor T4 and a conductor 46 which connects their terminal to thepositive voltage supply conductor 39. Resistors R17 and R18 provide theforward bias voltage for a transistor T5 whose base is connected to thejunction of resistors R17 and Rl. Thus whena signaly of suliicientamplitude to pass the threshold occurs, the transistor T is caused tobecome conductive through its emitter-collector circuit.

The pulse-amplier 33 comprises transistors T4 and T5 together with theirrespective collector and emitter circuits. Transistor TS, which might beconveniently of the'ZN 328A type, has its emitter coupled to conductor46 (the positive voltage supply) through a resistor R19v deliversamplified pulses to capacitor Clit.

As hereinbefore described, the integrator 39 accepts signal energy fromthetcontinuous channel in the form of a voltage which is averaged over atime period. Vfhen the integrator output voltage, which represents theintegrated input signal voltage and appears across the terminals ofcapacitor Cil, reaches a predetermined value, the voltage sensitivedetector 34 will respond and actuate alarm relay 35. Thus the hounds ofan electric drill or the scraping away of the mortar between the bricksof a` vault wall will build up, even though interrupted at intervals,until the alarm level is attained. The impact channel', on the otherhand, will respond instantly through the integrator to produce an alarmsignalfupon the occur-r rence of a single violent impact sound but willnot produce a false alarm upon a single light impact sound due to thesuppression effect of the threshold. Furthermore, impact sounds whichare above the threshold but below the alarm level are integrated withthe result that signals are stored in the integrator so that repetitionthereof will produce an alarm. An additional feature of the thresholdrcontrol is the provision of the variable resistor RM which permitsadjustment of the circuit so that an alarm will occur upon a discretenumber of blows of a given intensity.

The voltage sensitive detector 34 comprises a unijunction transistor (ordouble base diode) T6, which may be of the 2N-490` type. The base Bl oftransistor T6 ls coupled to conductor 39 through a resistor R21 and thebase B2 is connected directly to conductor 4d. The emitter is alsocoupled to conductor 46 through the series combination of the coil ofthe alarm relay 35 and resistor R13, while the junction of the alarmrelay 35 and resistor R13 is connected to the positive terminal ofcapacitor C711.

Unijunction transistor T6 will not conduct until the voltage between itsemitter and base Bl equals or eX- ceeds a predetermined percentage ofthe voltage between bases B1 and B2 thereof, e.g. 60%. ln other words,the unijunction transistor will not conduct until a predetermined signalvoltage is supplied to the emitter of transistor T6 from capacitor Clitof the integrator 30. Resistor R21 reduces the normal volt potentialbetween conductors 39 and 40 to approximately 9 volts at the base B1.Thus, when the voltage on capacitor Cll reaches 60% of 9 volts(approximately 5.5 volts), the transistor T6 will become conductive.

When transistor T6 becomes conductive, an energizing circuit for thealarm relay 3S is momentarily completed and the relay is energizedthereby operating the transfer contacts 46 which in turn actuateconventional alarm annunciating devices (not shown) as is well known inthe art.

Practical experience with unijunction transistors when utilized asdescribed above has shown that a false alarm hazard exists when a dip inthe voltage supply occurs at f falls to a G a time when there is acharge on capacitor C11.Since the transistor becomes conductive when theemitter-base Bl voltage reaches a certain percentage of base Bit-base B2voltage, this condition may be attained by a decrease of the Bl-BZvoltage as readily as by increase of the emitter-base El voltage as isintended. Consequently, at n some time when random sounds have causedcapacitor Cil to become charged to a voltage less than the alarm level,say 4 volts, a dip in the Bil-BZ: voltage from the normal i9 volts toabout 6.5 volts will result in the production of a false alarmindication.

yThe present invention is protected against such contingency by thesuppressor circuit 35 comprising the conductor 47 which connects thecollector of transistor T5 through rectifiers REC l@ and REC il, whichboth might be of the iN 2070 type, to the junction of resistors R22 andR23twhich act as a voltage divider for the potential supplied at theterminals 4l and 42. The purpose of this connection is to allow thecharge on capacitor C11 to be dissipated to ground when the power supplyvoltage predetermined value via the pathof conductor 57 and resistor R23to the ground conductor 40. Resistors R22 and R23 are selected so thatthe voltage at their junction is somewhat above the 5.5 firing voltageof the unijunction transistor T5, say 7 volts, and rectilier REC ll.will conduct in the forward direction when the voltage at the junctionof resistors R22 and R23 is less than the voltage on capacitor Cil'.Thus, when a dip in the supply voltage reduces the potential at theresistor B22-R23 junction to a value less than that atthe capacitor, thecapacitor Clt ywill discharge through conductor i7 thereby preventing afalse alarm indication.

Rectifier REC l@ is provided to prevent discharge of the capacitor Cilinto'the collector of transistor T5 while rectifier REC 12 prevents thedischarge of capacitors C3 and C2i into resistors R22 and R23. While thepresence of capacitors C3 and C4 provide a delaying effect and thus helpprevent a supply voltage dip from arriving at tne unijunction transistorTdbeforethe suppressor circuit has had time to discharge capacitor C11,another capacitor C13 is connected between the bases B1 and B2 oftransistor T6 to further slow the effect of voltage dips upon thetransistor.

While the invention has been described in connection with a specificembodiment thereof and in a specific use, various modifications thereofwill occur to those skilled in the art without departing from the spiritand scope of the invention as set forth in the appended claims.

What is claimed is:

ll. An electrical protection system for detecting physical attacks on avault or like structure, comprising:

(l) vibration transducer means disposed in close proximity to a surfaceof the structure to be protected so as to be subject to accelerationresulting from vibratory energy in the structure walls and arranged toproduce an alternating output voltage proportional to the magnitude ofthe acceleration to which it is subjected;

(2) a first amplifier coupled to the output of said transducer means;

(3) a continuous signal Channel comprising:

(a) a second amplifier having a dynamic range selected to accommodateinput signals corresponding to signal voltages characteristic ofrelatively low-noisedevcl attacks on said structure;

(b) a sensitivity control for adjusting the input level to said secondamplifier;

(c) means to supply the output of said first amplifier to the input ofsaid second amplifier; and

(d) rectifier means coupled to the output of said second amplifier forproducing a irst direct voltage proportional to the amplitude of saidsignal voltage;

(4) an impact signal channel comprising:

(a) a rectifier circuit;

(b) means to supply the output of said first amplifier to said rectifiercircuit to produce a second direct voltage proportional to the amplitudeof said signal voltage;

(c) a threshold control coupled to the output of said rectifier circuitto suppress values of said second direct voltage below a preselectedthreshold value, said threshold value being substantially greater thanthe input voltage resulting from a signal voltage level characteristicof a relatively low-noise-level attack on said structure; and

(d) means coupled to said threshold control to produce direct voltagepulses proportional in amplitude and duration to values of said seconddirect voltage passed by said threshold control;

() an integrating circuit having a relatively long time constant;

(6) means to apply said first direct voltage and said direct voltagepulses to said integrating circuit whereby the latter integrates saidfirst direct voltage and said direct voltage pulses; and

(7) alarm signalling means coupled to said integrating circuit andarranged to produce an alarm signal indication When the energy stored insaid integrating circuit exceeds a predetermined value.

2. An electrical protection system for detecting physical attacks on avault or like structure, comprising:

(l) a plurality of vibration transducers disposed in close proximity tothe inside surfaces of the structure to be protected so as to be Subjectto acceleration resulting from vibratory energy in the structure Wallsand each arranged to produce an alternating output voltage proportionalto the magnitude of the acceleration to which it is subjected;

(2) means coupled to said transducers to combine said output voltagesinto a composite signal voltage proportional to the intensity ofvibrations in said walls;

(3) a peaking circuit coupled to the output of said last mentioned meansand arranged to provide a peak response at approximately the naturalfrequency of said transducers, a smoothed response at frequencies in theoutputs of said transducers above said natural frequency and a sharplyattenuated response at frequencies in the outputs of said transducerssubstantially below said natural frequency;

(4) a first amplifier coupled to the output of said peaking circuit;

(5) a continuous signal channel comprising:

(a) a second amplifier having a dynamic range selected to accommodateinput signals corresponding to composite signal voltages characteristicof relatively low-noise-level attacks on said structure;

(b) a sensitivity control for adjusting the input level to said secondamplier;

(c) means to supply the output of said first amplifier to the input ofsaid second amplifier; and

(d) a voltage doubler-rectifier circuit coupled to the output of saidsecond amplifier for producing a first direct voltage proportional tothe amplitude of said composite signal voltage;

(6) an impact signal channel comprising:

(a) a rectifier circuit;

(b) means to supply the output of said first amplifier to said rectifiercircuit to produce a second direct voltage proportional to the amplitudeof said composite signal voltage;

(c) a threshold control coupled to the output of said rectifier circuitto suppress values of said second direct voltage below a preselectedthreshold value, said threshold value being substantially greater thanthe input voltage resulting from a combined signal voltage levelcharacteristic of a relatively low-noise-level attack on said structure;

(d) means to adjust said threshold value; and

(e) means coupled to said threshold control to produce direct voltagepulses proportional in amplitude and duration to values of said seconddirect voltage passed by said threshold control;

(7) an integrating circuit having a relatively long time constant;

(8) means to apply said first direct voltage and said direct voltagepulses to said integrating circuit Whereby the latter integrates saidfirst direct Voltage and said direct voltage pulses; and

(9) alarm signalling means coupled to said integrating circuit andarranged to produce an alarm signal indication when the energy stored insaid integrating circuit exceeds a predetermined value.

3. An electrical protection system for detecting physical attacks on avault or like structure, comprising:

(l) a plurality of vibration transducers disposed in close proximity tothe inside surface of the structure to be protected so as to be subjectto acceleration resulting from vibratory energy in the structure wallsand each arranged to produce an alternating output voltage proportionalto the magnitude of the acceleration to which it is subjected;

(2) means coupled to said transducers to combine said output voltagesinto a composite signal voltage proportional to the intensity ofvibrations in said walls:

(3) a peaking circuit coupled to the output of said last mentioned meansand arranged to provide a peak response at approximately the naturalfrequency of said transducers, a smoothed response at frequencies in theoutputs of said transducers above said natural frequency and a sharplyattenuated response at frequencies in the outputs of said transducerssubstantially below said natural frequency;

(4) a first amplifier coupled to the output of said peaking circuit;

(5) a continuous signal channel comprising:

(a) a second amplifier having a dynamic range selected to accommodateinput signals corresponding to composite signal voltages characteristicof relatively low-noise-level attacks on said structure;

(b) a sensitivity control for adjusting the input level to said secondamplifier;

(c) means to supply the output of said first amplifier to the input ofsaid second amplifier; and (d) a voltage doubler-rectifier circuitcoupled to the output of said second amplifier Afor producing a firstdirect voltage proportional to the amplitude of said composite signalvoltage;

an impact signal channel comprising:

(a) a rectifier circuit;

(b) means to supply the output of said first amplifier to said rectifiercircuit to produce a second direct voltage proportional to the amplitudeof said composite signal voltage;

(c) a threshold control coupled to the output of said rectifier circuitto suppress values of said second direct voltage below a preselectedthreshold value, said threshold value being substantially greater thanthe input voltage resulting from a combined signal voltage levelcharacteristic of a relatively low-noise-level attack on said structure;

(d) means to adjust said threshold value; and

(e) means coupled to said threshold control to produce direct voltagepulses proportional in amplitude and duration to values of said seconddirect voltage passed by said threshold control;

(7 an integrating circuit including a capacitor and a 11 resistiveelement connected so as to discharge said capacitor, said integratingcircuit having a relatively long time constant of the order of 15-25minutes; (8) means to apply said iirst direct voltage and said directvoltage pulses to said capacitor to charge the latter whereby saidintegrating circuit integrates said first direct voltage and said directvoltage pulses; (9) a source of direct voltage operating potential; and(10) alarm signalling means coupled to said integrating circuit andarranged to produce an alarm signal indication when the voltage acrosssaid capacitor exceeds a predetermined value, said alarm signallingmeans comprising:

(a) a unijunction transistor;

(b) an alarm relay having an energizing coil and signalling contacts;

(c) means to apply said operating potential to the respective bases ofsaid unijunction transistor; and

(d) means including the coil of said alarm relay to couple saidcapacitor between the emitter and one of the bases of said unijunctiontransistor whereby the latter will conduct and energize said alarm relaywhen the voltage across said capacitor exceeds said predetermined value.

4. An electrical protection system as set forth in claim 3 comprisingvoltage sensitive means coupled to said capacitor and to said source ofdirect operating potential and arranged to provide a discharge path forsaid capacitor when said operating potential drops to a selectedproportion of its normal value thereby to prevent conduction of saidunijunction transistor and energization of said alarm relay uponoccurrence of a substantial dip in said operating potential with apartial charge on said capacitor such that the voltage thereacross issubstantially below said predetermined value.

5. An electrical protection system as set forth in claim 4 comprising anadditional capacitor coupled between the bases of said unijunctiontransistor.

References Cited UNITED STATES PATENTS 2,799,015 7/1957 Bell 340-2612,806,082 9/1957 Woods 340-261 X 3,016,457 1/1962 Brown et al. 340-261 X3,069,672 12/1962 Rau 340-261 3,134,970 5/1964 Kelly et al 340-2613,147,467 9/1964 Laakmann 340-261 THOMAS B. HABECKER, Acting PrimaryExaminer.

NEIL C. READ, Examiner.

D. L. TRAFTON, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent N6.3,364,477 January 16, 1968 Vincent T. McDonough It is hereby certifiedthat error appears in the above numbered patent requiring correction andthat the said Letters Patent should read as corrected below Column l,line Z8, for "system" read systems column 3, lines 3 and 4, for "Bmorph"read bimorph n; column 6, line l0, for "dynamic" read dynamite column 7,line 28, for "hounds" read sounds column 8, line l0, for "19 volts" read9 volts U; column 9, line 32, for "surfaces" read surface column 10,line 50, for "walls:" read walls;

Signed and sealed this 4th day of March 1969.

(SEAL) Attest:

Edward M. Fletcher, J r. EDWARD J. BRENNER Attesting OfficerCommissioner of Patents

